Starwatch: July diary

The Summer Triangle of Vega, Altair and Deneb dominates the high S sky at the star chart times. At nightfall, though, Venus blazes at mag -4.0 to be by far the brightest of four bright objects that line up in the W. Look to the left of Venus, and a little higher, for Regulus in Leo, and farther in the same direction for Mars and Saturn. July sees the trio of planets draw together but also sink lower into the twilight. Saturn (mag 1.1) moves only a little in W Virgo and is being caught by Mars (mag 1.3 to 1.5) which lies 1.8° below Saturn by 31 July. Venus, chasing them both as it brightens to mag -4.2, sweeps 1.1° N of Regulus on the 10th and stands 8° below and to the right of the Mars-Saturn pair by the month's end. A telescope at midmonth shows Venus as a 17 arcsec and 65% sunlit gibbous disc, while Mars is only 5 arcsec wide and Saturn is 17 arcsec across, with rings that are 38 arcsec wide and tipped at 3°. Jupiter improves from mag -2.5 to -2.7 and (not counting the Moon) is the most conspicuous object in the E to SE before dawn. Rising in the E by 01:00 tomorrow and two hours earlier by July's end, it is slow moving in Pisces, S of the Square of Pegasus, where it lies below the Moon next Sunday morning and again on 31 July. Uranus, a mag 5.8 binocular object, lies 2° to 3° to the right of Jupiter. Though its brightening stalled near the fifth magnitude, Comet McNaught has been visible through binoculars, as it swept from right to left low across our N sky during recent weeks. It passed above Capella on 21 June and appeared as a small greenish blob with a dim upwards-pointing tail. Midnight BST tonight sees it 17° to the left of Capella and about 3° lower as it disappears into the twilight. A solar eclipse on 11 July is total along a path that crosses the S Pacific but is not visible from Europe. July diary 2nd 17h Comet McNaught at perihelion 4th 02h Moon 7˚N of Jupiter; 16h Last quarter 6th 12h Earth farthest from Sun (152 million km) 10th 04h Venus 1.1˚ N of Regulus 11th 21h New moon and total solar eclipse 15th 02h Moon 6˚ S of Venus 16th 06h Moon 6˚S of Mars; 20h Moon 8˚S of Saturn 18th 11h First quarter 24th 05h Jupiter stationary 26th 03h Full moon 31st 10h Moon 7˚ N of Jupiter 2 *Times are BST